CHEMICAL & ENERGY analysis
Speciation of Chlorinated Hydrocarbons
in Reformate using the Agilent
7200 GC/Q-TOF
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ABSTRACT
Sofia Nieto
The presence of chlorine in petroleum products can be harmful to equipment
and refining processes. In addition to total chlorine determination, hyphenated
techniques are needed to identify and quantitate the different chlorinated
species. Speciation of chlorinated hydrocarbons in reformate was performed
using the Agilent 7200 GC/Q-TOF high resolution mass spectrometer.
Using extracted ion chromatograms at accurate mass, excellent selectivity
and sensitivity were achieved, enabling the detection and quantitation
of chlorinated hydrocarbons in the very complex reformate matrix. These
compounds were determined at concentrations below 2 pg on-column,
corresponding to 0.5 ppm (mg/kg) in the reformate matrix.
Agilent Technologies, Santa Clara, USA
INTRODUCTION
Frank David, Bart Tienpont
and Pat Sandra
Research Institute for Chromatography,
Kortrijk, Belgium
Fabien Chainet, Michel Thomas
and Eric Lemaire
IFP Energies Nouvelles, Solaize, France
The presence of chlorine in the petroleum industry is of considerable
importance because of the potential formation of hydrogen chloride in liquid
or gas streams [1]. This chloride-containing gas can deactivate downstream
catalysts and cause undesired reactions. Chlorine is a poison recovered on
Pd/Al2O3 catalysts during selective hydrogenation [2]. The presence of HCl
in a hydrocarbon matrix leads to the formation of chlorinated hydrocarbons
and can also promote the polymerization of olefins to produce “green” oils,
mainly containing C6-C18 hydrocarbons [3]. Even if the concentration of HCl is
relatively low, it can still interfere with operating processes that use hydrogen
and can also cause corrosion problems in equipment such as pipes, valves
and compressors.
In addition, HCl is considered a hazardous material and must be eliminated before release to the environment [1].
Recently, a review on total chlorine determination was published by Doyle et al. [4]. Chlorine can be measured using
X-ray fluorescence (XRF) with a quantitation limit (LOQ) of 4 mg/kg in petroleum products and derivatives [5], by
ICP-OES [4] and also by ICP/MS [6]. Micro-coulometric methods are currently the most widely used techniques for the
determination of total chlorine, using standard test methods ASTM D4929 [7] or NF EN 14077, with an LOQ of around
1 mg/kg (ppm).
However, these methods determine the total chlorine concentration rather than identifying specific organochlorine
compounds. In the petroleum industry, speciation of chlorine is necessary as these compounds need to be identified
and quantitated, in order to develop systems for trapping these molecules. To our knowledge, there are no speciation
methods for chlorine in petroleum products available in the literature.
Typically, chlorinated organic compounds are analyzed by gas chromatography (GC) and liquid chromatography (LC)
coupled to mass spectrometry or specific detectors such as electron capture detector (ECD), atomic emission detector
(AED) and inductively coupled plasma mass spectrometry (ICP/MS). GC-ECD lacks specificity and the ECD detector
response is strongly dependent on the organic molecule [8, 9]. Chlorobenzene, for instance, gives a very low response in
ECD. GC-AED can also be used, but chlorine detection is not very sensitive and the co-elution of hydrocarbons at very high
levels (3-4 orders of magnitude higher than the chlorine compounds) exceeds the selectivity of the detector [10]. Despite
spectral interferences at m/z 35 and low ionization potential for chlorine, GC-ICP/MS can be performed, as shown by
Peters et al. [11], for the detection of three compounds (dichloromethane, trichloroethane and trichloroethylene) in
pentane with LODs around 2 mg/L. However, GC-ICP/MS configurations are not widely available.
Due to the complexity of reformate samples, containing about 250 hydrocarbon species, and the chlorine concentration at
low (or sub-) ppm level, selective and sensitive techniques must be used. Compound specific analysis can be performed
using two-dimensional GC (heart-cutting) [12] or GC-MS/MS in multi-reaction monitoring (MRM) mode [13]. However,
these techniques can only be applied to selected target compounds that are available as standards and for which
retention time and mass spectra (MRM transitions) can be determined. In organochlorine speciation, the availability
of a screening (non-target) method that allows for the detection and quantitation of chlorinated hydrocarbons (alkanes
and aromatics) in gasoline, naphtha or reformate samples at low ppm levels would offer interesting possibilities for the
petrochemical industry.
In this application note, the use of the Agilent 7200 GC/Q-TOF high resolution mass spectrometer for the analysis
of chlorinated hydrocarbons in reformate is described. Ion extraction at accurate masses is used for detection and
quantitation of the target compounds.
EXPERIMENTAL
Samples: A reformate sample from IFP Energies Nouvelles (Solaize, France) was used as the test matrix. Basic properties
of this reformate are listed in Table 1. A stock solution of 10 chlorinated hydrocarbons was prepared in heptane at a
concentration of 100 mg/kg (ppm). The reference compounds are listed in Table 2. A diluted stock solution was also
prepared in heptane at 10 ppm. Spiked matrix solutions at concentrations between 0.5 and 20 ppm (per chlorinated
compound) were prepared by spiking the reformate test matrix with the stock solution.
GC/Q-TOF instrument:
Analyses were performed on an Agilent 7890B GC equipped with a split/splitless inlet. Injection was performed using
an Agilent 7693 ALS. The GC was coupled to an Agilent 7200 Q-TOF mass spectrometer.
Analytical conditions:
0.2 µL of sample was injected in split mode (1/50) at 250°C. Separation was performed on a 100 m x 0.25 mm ID x 0.5
µm HP-PONA column (19091Z-530). The carrier gas was helium at 1.5 mL/min constant flow. The oven was programmed
from 35°C (5 min) at 4°C/min to 250°C (10 min). The transfer line was set at 280°C.
The 7200 Q-TOF was operated in MS mode using electron impact (EI) ionization. The source temperature was 230°C. The
scan rate was 5 Hz in HR (high resolution) mode and the mass range was 50 to 300 amu. No internal mass referencing
was used, but the instrument was mass calibrated before each run using the keyword command (MassCal) in the
sequence.
2
Results and discussion
The total ion chromatogram obtained for the analysis of the diluted calibration stock (10 ppm) is shown in Figure 1.
Taking into account the injection volume (0.2 µL) and the split ratio (1/50), the injected amount corresponds to 40 pg
per compound on-column. Seven compounds were easily detected. However, compounds 2, 3 and 4 were masked by
the heptane solvent peak. For the detected compounds, accurate mass spectra were obtained and searched against the
standard NIST library. The chloroalkanes from chloropentane to chlorononane, all have the ion at m/z 91.031 in common.
Fig 1: Base Peak Chromatogram of the analysis of a test solution containing chlorinated
hydrocarbons in heptane (10 ng/µL concentration, 40 pg on-column).
Using the formula generator option, this fragment ion was correctly identified as [C4H8Cl]+, as illustrated by the high
resolution mass spectrum of chloroheptane (compound 7) in Figure 2. At m/z 93.028 the chlorine isotope peak is
detected. For these ions, the mass error was found to be lower than 4 ppm.
Fig. 2: High resolution accurate mass spectrum of peak 7 (1-chloroheptane)
Using extracted ion chromatograms at accurate mass, very high selectivity can be obtained. This is illustrated in Figure
3. In Figure 3A, the total ion chromatograms are compared for a reformate sample (top) and the same reformate sample
spiked at 1 ppm level with the chloroalkanes (bottom). These profiles show the high complexity of the reformate
sample, mainly containing aromatic hydrocarbons (toluene, xylenes, C3-, C4-, C5- benzenes) and paraffins. If the ion
chromatograms are extracted using a window of +/- 0.5 amu, as is done on low resolution instruments such as a single
quadrupole or a triple quadrupole instruments, the chloroalkane compounds cannot be selectively detected in the spiked
sample.
3
Fig. 3A: Comparison of TIC obtained for reformate sample (top) and reformate sample spiked at
1 ppm level with chlorinated hydrocarbons (bottom).
Fig. 3B: Comparison of EIC obtained for reformate sample (top) and reformate sample spiked
at 1 ppm level with chlorinated hydrocarbons (bottom). EIC performed at unit mass resolution
(91.0309 +/- 0.5 amu)
Fig. 3C: Comparison of EIC obtained for reformate sample (top) and reformate sample spiked
at 1 ppm level with chlorinated hydrocarbons (bottom). EIC performed at high mass resolution
(91.0309 +/- 20 ppm)
4
This is illustrated in Figure 3B, showing the EIC at m/z 91.0309 +/- 0.5 amu. No difference can be observed between the
sample (top) and the spiked sample (bottom). The main peaks detected in these EICs are the aromatic hydrocarbons that
give the well know tropylium ion at m/z 91 in their mass spectra. This fragment corresponds to [C7H7]+ and the exact
mass is 91.0542. The first 4 peaks correspond to toluene (19.5 min), ethylbenzene, m- and p- xylene and o-xylene (24 - 26
min). These compounds all have the tropylium ion as the most abundant ion in their mass spectra and low resolution MS
is unable to differentiate the tropylium ion from the [C4H8Cl]+ ion. If ions are extracted at a mass accuracy of +/- 20 ppm,
the target compounds can be selectively detected, as illustrated in Figure 3C. In the unspiked sample, no chloroalkanes
were detected (top chromatogram), while compounds 6, 7, 9 and 10 were detected in the spiked sample.
The EIC signals at accurate mass for a standard (10 ppm of compounds in heptane, corresponding to 40 pg on-column)
and for a spiked matrix sample (10 ppm compounds in matrix) are compared in Figure 4. The peak areas are quite similar,
indicating that no quenching or ion suppression occurs in the matrix. Only slight differences are noted in retention time
and peak width, caused by matrix effects on the chromatography (solvent effects).
Using this method, all chlorinated compounds were detected at low ppm or even sub-ppm levels in the matrix (low
ppb levels on column). To take maximum advantage of the selectivity, the ions chosen for EIC extraction all contained
chlorine (see Table 2). Even though in some cases chlorine-containing ions were of relatively low abundance in a
compound spectrum, it allowed efficient detection of the compounds in the very complex matrix. This is illustrated in
Figure 5 for chlorobenzene using the ion at 112.007 and in Figure 6 for benzylchloride using the ion at m/z 126.023. Ion
chromatograms were extracted at +/- 20 ppm m/z window. The high resolution mass spectra are shown in these figures
and the mass accuracy was calculated using the formula generation option. Chlorobenzene showed a mass error of -3.03
ppm and benzylchloride a mass error of -3.17 ppm. It should be emphasized that these mass errors were obtained in the
complex reformate matrix.
Fig. 4: Comparison of EIC obtained for a 10 ppm standard solution (top) and reformate sample
spiked at 10 ppm level with chlorinated hydrocarbons (bottom). EIC performed at high mass
resolution (91.0309 +/- 20 ppm)
5
Fig. 5: Detection of chlorobenzene in reformate (spiked at 10 ppm level) - EIC @112.0074 +/- 20 ppm
Mass spectrum is given in insert
Fig. 6: Detection of benzylchloride in reformate (spiked at 10 ppm level) - EIC @126.0231 +/- 20 ppm
Mass spectrum is given in insert
6
Properties
Methods
Values
Density (g/cm3)
NF EN ISO 12185
0.8316
Boiling range (◦C)
ASTM D2887
82-197
RON
101
Paraffins (%wt)
5.0
Isoparaffins (%wt)
14.7
Naphthenes (%wt)
IFPEN 9302
1.1
Aromatics (%wt)
78.4
Olefins (%wt)
0.8
Chlorine (mg/kg)
NF EN 14077
<2
Table 1
peak
tR (min)
solute
1
9.949
2-chloro-2-methylpropane
2
16.463
1-chloro-2-methylbutane
3
16.747
2-chloro-pentane
4
18.784
1-chloropentane
5
23.390
chlorobenzene
6
23.955
1-chlorohexane
7
28.834
1-chloroheptane
8
30.921
benzylchloride
9
33.334
1-chlorooctane
10
37.484
1-chlorononane
formula
C 4H9Cl
92
77.0158
106
62.9996
106
62.9996
C 5H11Cl
106
62.9996
112
112.0074
C6H13Cl
120
91.0309
C7H15Cl
134
91.0309
126
126.0231
C 8H17Cl
148
91.0309
162
91.0309
C6H5Cl
C7H7Cl
C 9H19Cl
7
exact mass
C 5H11Cl
C 5H11Cl
Table 2
MW
fragment
C 3H6Cl
C 2H4Cl
C 2H4Cl
C 2H4Cl
C6H5Cl
C 4H8Cl
C 4H8Cl
C7H7Cl
C 4H8Cl
C 4H8Cl
CONCLUSION
Sub-ppm chlorinated hydrocarbons can be analyzed in reformate samples using GC/Q-TOF high resolution MS analysis.
The high selectivity offered by accurate mass ion extraction allows the target compounds to be detected and quantified
in this extremely complex matrix. Sensitivity is better than 2 pg on column, corresponding to 0.5 ppm (mg/kg) in the
reformate matrix.
References
[1] O.K. Karan, M.A. Ay, K. Karhaman, A. Selmen, “Combating
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[3] J. Cosyns, O. Ducreux, Q. Debuisschert, and F. Lepeltier,
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review”, Spectrochim. Acta B, 2013, 86, 102.
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[7] ASTM D4929, Standard Test Methods for Determination
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[10] C. Brede, S. Pedersen-Bjergaard, “State-of-the art of
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[11] G.R. Peters, D. Beauchemin, “Versatile interface for
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[12] F. Chainet, C.P. Lienemann, J. Ponthus, M.
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[13] N.S. Chary, S. Herrera, M.J. Gómez, A.R. FernándezAlba, “Parts per trillion level determination of endocrinedisrupting chlorinated compounds in river water and
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Published in USA, March 26, 2015
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